DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 115 



306. To illustrate these general views as to the develop- 

 ment of the embryo, we will briefly describe the principal 

 phases, as they have been observed in the White-fish of 

 Europe, which belongs to the salmon family. The follow- 

 ing magnified figures will illustrate this development, and 

 show the successive appearance of the different organs. 



Fig. 111. 



Fig. 112. 



Fig. 113. 



307. The egg when laid (Fig. Ill) is spherical, about 

 the size of a small pea, and nearly transparent. It has no 

 albumen, and the shell-membrane is so closely attached to 

 the membrane of the yolk, that they cannot be distinguished. 

 Oil-like globules are scattered through the mass of the yolk, 

 or grouped into a sort of disc, under which lies the germina- 

 tive vesicle. The first change in such an egg occurs a few 

 hours after it has been laid, when the shell-membrane 

 separates from the yolk-membrane, in consequence of the 

 absorption of a quantity of water (Fig. 112). Between the 

 shell-membrane (sm), and the yolk (?/), there is now a con- 

 siderable transparent space, which corresponds, in some 

 respects, to the albumen found in the eggs of birds. 



308. Soon afterwards we see, in the midst of the oil-like 



Fig. 114. 



Fig. 115. 



Fig. 110. 



globules, a swelling in the shape of a transparent vesi- 

 cle (Fig. 113, g), composed of very delicate cells. This is 

 the first indication of the germ. This swelling rapidly en- 

 larges until it envelops a large part of the yolk, when a 



